The present invention relates to railroad frogs and more particularly to a rail frog designed to support a railroad wheel to travel through the frog on its flange rather than its tread.
During the period of modern railroading, whenever it was necessary for one rail to cross over another, as in a turnout or crossing, it was almost exclusively accomplished with a fixed point frog. Originally these frogs were fabricated basically of rail sections, flangeway filler bars and blocks bolted together. This fixed point frog requires the railroad wheel tread and flange to attempt to "jump" across the flangeway of the other rail; i.e., to traverse the intersecting flangeway gap without any support. As a result, each wheel delivers a severe impact to the small surface area of the point of the frog, generating great stress and wear at the point. The point of the frog has become a locus of maintenance and repair effort.
As the railroad tonnage increased it was necessary to develop frogs constructed wholly or partially of cast manganese. These frogs are much more expensive but have come into common usage because they can better resist the severe impacts imposed on the frog point. However, the flangeway gap with its inherent impacts still exist, causing passenger discomfort and damage to equipment, roadbed and the frog itself.
In an attempt to increase passenger comfort on light weight transit systems, designs for cast manganese frogs have been modified to allow wheels to pass over the flangeway gap by riding on their flanges. This is accomplished by diminishing the flangeway depth in the area of the gap to the point that the flange is not only riding upon it, but has lifted the tread slightly above the top of rail. The lifting is accomplished by ramping the flangeway from both ends. This design has been successfully used in transit railways but has not been tested under heavy railroad loads. The main problem with this design is its high cost, due to the fact that the entire transition typically is fabricated in cast manganese for strength and stability. Thus new blanks and molds must be made for each different angle of crossing, and each crossing is virtually a one-of-a kind installation formed of custom components.